Multiple sclerosis (MS) is a human CNS demyelinating disease of unknown cause. The role of B cell immunity in disease pathogenesis is unknown, but has gained renewed interest because of pathology indicating IgG- mediated demyelination and the effective treatment of MS with anti-B cell therapies. Clues to the nature of disease are indicated by increased and persistent intrathecal IgG synthesis and the presence of oligoclonal bands (OCBs). OCBs are not unique to MS and in known infectious diseases of the CNS represent antibody (Ab) to the disease-causing agent, providing a rationale for our hypothesis that the oligoconal IgG in MS is directed against disease-relevant antigens. Whether the primary role of B cells in MS pathogenesis is through their effector antibody molecules, in cytokine production or as antigen-presenting cells, it operates through antigen binding to unique and disease-specific B cell surface Ig receptors. The goals of this proposal are to identify the antigenic targets of MS CSF OCBs and to define how B cells targeting these antigens contribute to disease pathogenesis. We developed a single cell RT-PCR protocol to efficiently amplify the heavy (VH) and light (VL) chain variable regions expressed by sorted MS CSF CD138+ plasma cells. Repertoires generated from CD138+ cells of MS patients each displayed seminal features of a T cell-dependent, antigen-driven response including clonal expansion, somatic hypermutation and biased use of VH4 germline segments. The phenotype of CSF CD138+ cells is that of short-lived plasma blasts and serial CSF repertoires show a persistent dynamic B cell response indicative of ongoing antigenic stimulation and not bystander activation. We have verified a mammalian expression system to produce recombinant IgG1 Abs that faithfully duplicates the in vivo pairings of plasma cell heavy- and light-chain V region sequences. Multiple MS rAbs have been demonstrated to bind oligodendrocyte antigens and myelin- enriched glycolipids. Aim 1 will identify epitopes recognized by Abs derived from MS CSF plasma blasts and will develop antigen-specific assays to screen other MS rAbs, MS CSF and inflammatory control CSF for specificity. Immunoassays including confocal microscopy, FACS sorting, and ELISA will be developed to assess the specificity and sensitivity of Ab responses to putative MS antigens. Aim 2 will investigate both long-term and acute effects of selected glycolipid- and glial cell-specific rAbs on CNS pathology with an emphasis on the measurement of inflammation, demyelination, oligodendroglial cell death, and axonal damage. Aim 3 will assess the effect of myelin- and glial cell-specific rAbs on oligodendrocyte cell differentiation and myelination using both cell culture and developing cerebellar explants. Identification of pathogenic MS-specific antigen(s) will have wide application, not only for early definitive diagnosis, but also for developing strategies to modulate and possibly prevent disease.